This invention relates to roadway impact attenuators or crash cushions used to protect the occupants of vehicles from direct impact with fixed roadside structures such as bridge abutments, piers, or the like. The preferred embodiments described below are to a great extent reusable, and are designed to absorb and harmlessly dissipate kinetic energy of an impacting vehicle with a minimum of structural damage to the impact attenuator itself.
Impact attenuation devices are often used to prevent cars, trucks and other vehicles from directly colliding with fixed structures positioned near or adjacent to a roadway. One approach to such impact attenuation devices utilizes expendable energy absorbing elements oriented in a linear array in front of the fixed highway structure. See, for example, the attenuation devices shown in Gertz U.S. Pat. No. 4,352,484 and VanSchie European Patent Doc. 0042 645. The attenuator disclosed in the Gertz patent utilizes a foamed honeycomb module to dissipate kinetic energy efficiently. The VanSchie document discloses a device utilizing axially oriented tubes which are crushed by an axially impacting vehicle. The device disclosed in the Gertz patent has achieved widespread commercial acceptance because it provides a highly efficient (and consequently compact) attenuation device. Of course, expendable energy absorbing elements must be replaced after impact. In some applications, the cost of such replacement may be considered excessive.
Another approach of the prior art focuses on low maintenance impact attenuators utilizing reusable energy absorbing elements. For example, Young U.S. Pat. No. 3,674,115 discloses a low maintenance impact attenuator that utilizes reusable fluid filled elastomeric buffer elements. Sicking U.S. Pat. No. 4,815,565 discloses a low maintenance impact attenuator that utilizes reusable elastomeric elements to resist axial collapse of the attenuator.
Low maintenance impact attenuators of the type shown in the Sicking patent do not obtain maximum efficiency from the reusable energy absorbing elements. This results in an attenuator that is relatively large, heavy, and expensive as compared to a comparable construction utilizing more efficient energy absorbing elements. Such low efficiency attenuators are unnecessarily costly, difficult to install, and prone to impact since they may intrude farther into a roadway. Such shortcomings may limit the application of low maintenance impact attenuators.
In particular, the elastomeric energy absorbing elements of the Sicking patent are shaped as thick walled cylinders. This shape requires relatively large volumes of elastomeric materials as well as relatively complex and expensive molding equipment. In addition, the cylindrical shape constrains the geometry of the impact attenuator. In particular, the thick walled cylindrical shape has a relatively low energy absorption capacity per pound of elastomeric material (efficiency) which results as described above in a longer, heavier, and higher cost impact attenuator.
It is therefore an object of this invention to provide a low maintenance impact attenuator that utilizes sheet members (preferably reusable elastomeric sheet members) as the energy absorbing elements, and to use such sheet members in a particularly efficient arrangement.
It is another object of this invention to provide a low maintenance crash cushion which is less costly, easier to install, shorter, and easier to maintain than prior art systems.
Another object is to provide an impact attenuator which utilizes bendable elastomeric sheets as energy absorbing elements.
Another object is to provide an impact attenuator utilizing elastomeric sheets as energy absorbing elements in such a way as to achieve unusually high energy absorption capacity per pound of elastomeric material.
Another object is to provide elastomeric energy absorbing elements for an impact attenuator, wherein the elements are shaped so as to be easily fabricated and inexpensive to produce.
Another object is to arrange bendable elastomeric elements in an impact attenuator such that the energy absorbing elements provide additional energy absorption through friction with other components of the attenuator.